Photovoltaic module cooling devices

ABSTRACT

A chip module cooling device includes two fluid circuits corresponding to inlet and outlet fluid circuits, respectively, wherein each comprises orifices and channel portions forming a tree structure, wherein branches represent the orifices, and nodes represent the channel portions, a branch linking a node to one child node only, wherein several nodes having a same parent node are sibling nodes and extends through L levels of the tree structure, with L≧3, and in fluidic connection with the other of the two fluid circuits, via channel portions corresponding to leaf nodes. For each fluid circuit, channel portions corresponding to sibling nodes are parallel to each other, and are not parallel to a channel portion corresponding to a parent node of the sibling nodes; and wherein channel portions of one of the fluid circuits are parallel to and interdigitated with channel portions of the other one of the fluid circuits.

PRIORITY

This application claims priority to Great Britain Patent Application No.1205732.9, filed Mar. 30, 2012, and all the benefits accruing therefromunder 35 U.S.C. §119, the contents of which in its entirety are hereinincorporated by reference.

BACKGROUND

The present invention generally relates to cooling devices forphotovoltaic receivers and photovoltaic receivers equipped with suchcooling devices.

Definitions of certain terms discussed herein are as follows:

Photovoltaics (PV) generate electrical power by converting solarradiation into direct current electricity through semiconductorsexhibiting the photovoltaic effect;

A photovoltaic cell (or PV cell, also “solar cell” or “photoelectriccell”) is a solid state device that converts energy of light directlyinto electricity by virtue if the photovoltaic effect;

A photovoltaic module (also “solar module”, “solar panel” or“photovoltaic panel”) is an assembly of connected photovoltaic cells;

A photovoltaic system typically includes an array of photovoltaicmodules, an inverter and interconnection wiring;

A thermal collector (also “solar thermal collector”) collects heat byabsorbing radiations, typically sunlight's;

A heat exchanger is a device/piece of equipment to efficiently transferheat from one medium to another;

In electronic systems, a heat sink is a component to cool a device bydissipating heat into a surrounding medium;

Solar thermal energy (STE) concerns technologies for harnessing solarenergy for thermal energy (heat). STE differs from and is acknowledgedto be much more efficient than photovoltaics, which converts solarenergy directly into electricity;

Concentrated solar power (also “concentrating solar power” or CSP)systems use mirrors or lenses that concentrate a large area of solarthermal energy onto a small area, such that electrical power (also“power”) can be produced when concentrated light is converted to heat,which drives a heat engine (e.g., a steam turbine) connected to a powergenerator. Common forms of concentration are: parabolic trough, dishStirlings, concentrating linear Fresnel reflector and solar power tower.

Concentrated photovoltaic (CPV) systems use optics (e.g., lenses) toconcentrate a large amount of sunlight onto a small area of solarphotovoltaic materials to generate electricity. Concentration allows forproduction of smaller areas of solar cells.

CPV should not to be confused with CSP: in CSP concentrated sunlight isconverted to heat, and then heat is converted to electricity, whereas inCPV concentrated sunlight is converted directly to electricity usingphotovoltaic effect;

Photovoltaic thermal hybrid solar collectors (also “hybrid PV/T systems”or PVT) are systems converting solar radiation into thermal andelectrical energy. Such systems combine a photovoltaic cell, whichconverts photons into electricity, with a solar thermal collector, whichcaptures the remaining energy and removes waste heat from the PV module.Two categories of PVT collectors are generally known:

PV/T fluid collector (air or liquid). In liquid collectors, a typicalwater-cooled design uses conductive-metal piping or plates attached tothe back of a PV module. The working fluid is typically water or glycol.The heat from the PV cells are conducted through the metal and absorbedby the working fluid, which assumes that the working fluid is coolerthan the operating temperature of the cells. In closed-loop systems thisheat is either exhausted (to cool it) or transferred at a heatexchanger, where it flows to its application. In open-loop systems, thisheat is used, or exhausted before the fluid returns to the PV cells;

PV/T concentrator (CPVT), wherein a concentrating system is provided toreduce the amount of solar cells needed. CPVT can reach very good solarthermal performance compared to flat PV/T collectors. However, mainobstacles to CPVT are to provide good cooling of the solar cells and adurable tracking system.

SUMMARY

In one embodiment, a chip module cooling device includes two fluidcircuits corresponding to an inlet fluid circuit and an outlet fluidcircuit, respectively, wherein each of the two fluid circuits comprisesan arrangement of orifices and channel portions forming a treestructure, wherein branches of the tree structure represent theorifices, and nodes of the tree structure represent the channelportions, a branch linking a node to one child node only, whereinseveral nodes having a same parent node are sibling nodes and extendsthrough L levels of the tree structure, with L≧3, and is in fluidicconnection with the other one of the two fluid circuits, via channelportions corresponding to leaf nodes of the tree structure; wherein, foreach of the two fluid circuits, channel portions corresponding tosibling nodes are parallel to each other, and are not parallel to achannel portion corresponding to a parent node of the sibling nodes; andwherein channel portions of one of the fluid circuits are parallel toand interdigitated with channel portions of the other one of the fluidcircuits.

In another embodiment, a photovoltaic receiver includes a photovoltaicmodule; and a cooling device, thermally connected to the photovoltaicmodule, the cooling device comprising two fluid circuits correspondingto an inlet fluid circuit and an outlet fluid circuit, respectively,wherein each of the two fluid circuits comprises an arrangement oforifices and channel portions forming a tree structure, wherein branchesof the tree structure represent the orifices, and nodes of the treestructure represent the channel portions, a branch linking a node to onechild node only, wherein several nodes having a same parent node aresibling nodes and extends through L levels of the tree structure, withL≧3, and is in fluidic connection with the other one of the two fluidcircuits, via channel portions corresponding to leaf nodes of the treestructure; wherein, for each of the two fluid circuits, channel portionscorresponding to sibling nodes are parallel to each other, and are notparallel to a channel portion corresponding to a parent node of thesibling nodes; and wherein channel portions of one of the fluid circuitsare parallel to and interdigitated with channel portions of the otherone of the fluid circuits.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows an exploded 3D view of a multilayer cooling device for aphotovoltaic device;

FIG. 2 focuses on a specific channel portion pattern, designed for agiven layer of the device of FIG. 1;

FIG. 3 depicts a 3D tree structure representing an arrangement oforifices and channel portions of a cooling device;

FIG. 4 shows a side view of a photovoltaic device mounted on a coolingdevice;

FIG. 5 is a 3D view of such a photovoltaic device, mounted on a coolingdevice;

FIG. 6 is a 3D view of a thermal collector for a photovoltaic device;

FIG. 7 is a partial view of FIG. 6, showing a section of the thermalcollector;

FIG. 8 is a section view of a photovoltaic thermal hybrid solarreceiver;

FIG. 9 is a section view of another photovoltaic thermal hybrid solarreceiver;

FIG. 10 is a side view of a photovoltaic thermal hybrid solar system;

FIG. 11 is a flowchart of steps implemented in methods of operation of aphotovoltaic thermal hybrid solar system such as depicted in FIG. 10;

FIGS. 12-13 are simplified representations of photovoltaic thermalhybrid solar systems;

FIGS. 14-15 are block diagram representations of additional photovoltaicthermal hybrid solar devices-based systems;

FIG. 16 is a graph showing the radiation intensity distribution at thelevel of an input plane of a hybrid receiver, while displacing thehybrid receiver along the optical axis of the system;

FIG. 17 is a graph showing the total irradiance captured by a thermalcollector and a PV chip of a hybrid receiver, while displacing thehybrid receiver along the optical axis of the system;

FIG. 18 is a graph comparing dispatched delivery of electrical power byvarious CPVT systems;

FIG. 19 is a simplified representation of a system for short-term localweather prediction using tracker solar sensor information; and

FIG. 20 schematically depicts an example of a control system—acomputerized unit, suitable for implementing steps of methods ofoperation of systems such as depicted in FIGS. 10, 12-15, and 19.

DETAILED DESCRIPTION

According to a first aspect, a chip module cooling device is disclosed,comprising two fluid circuits corresponding to an inlet fluid circuitand an outlet fluid circuit, respectively, wherein each of the two fluidcircuits includes an arrangement of orifices and channel portionsforming a tree structure, wherein branches of the tree structurerepresent the orifices; and nodes of the tree structure represent thechannel portions, a branch linking a node to one child node only,whereby several nodes having a same parent node are sibling nodes; andextends through L levels of the tree structure, with L≧3, and is influidic connection with the other one of the two fluid circuits, viachannel portions corresponding to leaf nodes of the tree structure, andwherein, for each of the two fluid circuits, channel portionscorresponding to sibling nodes: are parallel to each other; and are notparallel to a channel portion corresponding to a parent node of thesibling nodes, and wherein channel portions of one of the fluid circuitsare parallel to and interdigitated with channel portions of the otherone of the fluid circuits.

Embodiments of the invention may include one or more of the followingfeatures: at one or more levels of the tree structure, and for each ofthe two fluid circuits, channel portions corresponding to sibling nodesare parallel to channel portions corresponding to a grandparent node ofthe sibling nodes; at one or more levels of the tree structure, and foreach of the two fluid circuits, each of the channel portionscorresponding to sibling nodes extends along a direction which, togetherwith a direction of extension of a parent node of the sibling nodes,form a pair of skew lines, and, preferably, the channel portionscorresponding to sibling nodes span a plane parallel to the parent nodeof the sibling nodes; each of the two fluid circuits comprises, at eachlevel L_(l) of the L levels for which 1≦l≦L−1: N_(l) orifices of theorifices, each leading to a respective one of the channel portions; andN_(l) parallel channel portions, each of the N_(l) channel portionsenabling fluid distribution to B_(l+1) orifices of the next level,where: B_(l+1)=N_(l+1)/N_(l); B₂≧2 and B₃≧2; at a given level L_(m) ofthe L levels, where 2≦m≦L, positions of orifices of one of the fluidcircuits correspond to first discrete points of a first finite array,the first discrete points generated by a set of discrete translations Rdefined by R=n₁ a₁+n₂ a₂, where n₁ and n₂ are integers and a₁ and a₂ arelinearly independent vectors, and wherein: channel portions at the levelL_(m−1) extend along or parallel to a₁; and channel portions at levelsL_(m) extend along or parallel to a₂; and positions of orifices of theother one of the fluid circuits correspond to second discrete points ofa second finite array, translated from the first finite array by atranslation r defined by r=x₁ a₁+x₂ a₂, with 0<x₁<1 and 0≦x₂<1, andpreferably x₁=x₂=½; each of the two fluid circuits comprises, in atleast one level L_(l) of the L levels: N_(l) channel portions formingNc_(l) strictly parallel channel lines, with B_(l)=Nc_(l)≦N_(l), each ofthe Nc_(l) channel lines comprising channel portions arranged in-line,and wherein preferably Nc_(l)=B_(l); each of the two fluid circuitscomprises, at each level L_(l) of the L levels: N_(l) channel portionsforming B_(l) strictly parallel channel lines, each of the channel linescomprising B_(l−1) channel portions arranged in-line, and, preferably,at one or more of the L levels, channel portions in a given channel lineare connected to enable fluid communication from one channel portion toanother in the given channel line; at a given level L_(m) of the Llevels, where 1≦m≦L, Nc_(l) strictly parallel channel lines of the inletfluid circuit are interdigitated with Nc_(l) strictly parallel channellines of the outlet fluid circuit, each channel line of the inlet fluidcircuit being parallel to each channel line of the outlet fluid circuit.

At a given level L_(m) of the L levels and for each of the two fluidcircuits, at least some of the N_(m) channel portions have anon-constant cross-section, and preferably comprise an enlarged areavis-à-vis a respective one of the N_(m) orifices; at a given level L_(m)of the L levels, for example at level L₃: two sets of orifices, eachcomprising B_(m) orifices, are arranged in correspondence withrespective outermost channels of a previous level L_(m−1); and each ofthe B_(m) orifices of the two sets and/or each of their respectivechannel portions have reduced dimensions along a direction of extensionof the channels of level L_(m).

The cooling device further includes a heat transfer structure,configured to connect one of the fluid circuits to the other, whereinthe heat transfer structure preferably comprises silicon; the heattransfer structure includes heat transfer channel portions, each of theheat transfer channel portions connecting at least one channel portioncorresponding to a leaf node of the inlet fluid circuit to one channelportion corresponding to a leaf node of the outlet fluid circuit, andwherein, preferably, each heat transfer channel extends along adirection rotated, preferably by 90°, with respect to a direction ofextension of the channel portions that it connects; a cumulated width ofthe cross-sectional areas of all orifices of one of the levels issubstantially equal, subject to ±15%, to a cumulated width of thecross-sectional areas of all orifices of another one of the levels,preferably of all other levels; and one or more levels of the L levelsinclude two superimposed layers, a first one of the two superimposedlayers comprising the orifices as through holes, the second one of thetwo superimposed layers comprising channel portions as through holes,and, preferably, the two superimposed layers are made of differentmaterials;

According to another aspect, a photovoltaic receiver includes aphotovoltaic module and a cooling device according to any one of theabove embodiments, thermally connected to the photovoltaic module.

Devices, systems, methods of operating such devices and systems, as wellas computer program functions partly implementing embodiments of thepresent invention will now be described, by way of non-limitingexamples, and in reference to the accompanying drawings.

The present invention forms part of comprehensive CPVT solutions. Suchsolutions revolve around novel photovoltaic thermal hybrid receivers.Aspects of these solutions concern such receivers, cooling devices forsuch receivers, photovoltaic thermal hybrid systems and operationmethods.

The present invention proposes novel systems and methods for operating aphotovoltaic thermal hybrid system. Such systems and methods rely on ahybrid solar receiver, equipped with a photovoltaic (or PV) modulecapable of delivering an electrical output power, and a thermalcollector distinct from the PV module. The PV module and/or the thermalcollector are movably mounted in the system. Furthermore, a collectorthermal storage is (thermally) connected to the thermal collector, inorder to store heat collected at the latter. In addition, positioningmechanism are provided, which are adapted to move the PV module and/orthe thermal collector. Then, instructing the positioning mechanism tomove the PV module and/or the thermal collector results in changing theratio of the intensity of radiation received at the PV module to theintensity received at the thermal collector. Thus, excess radiationreceived at the PV module (i.e., larger than necessary to meet a powerdemand) can advantageously be used to heat up the thermal circuit andstore heat at the thermal storage.

The accompanying drawings are organized as follows:

Cooling devices 25 such as depicted FIG. 1-4 can advantageously be usedto cool PV receivers, as shown in FIGS. 4 and 5. PV receivers 21 canadvantageously be complemented by thermal collectors 22 such as depictedin FIGS. 6, 7. This results in hybrid receivers such as depicted inFIGS. 8, 9. The hybrid receivers can in turn be used in systems 10 suchas depicted in FIGS. 10, 12-15.

The systems 10 can be complemented to enable short-term weatherprediction, FIG. 19. The above systems 10 can be operated according to amethod such as captured in the flowchart of FIG. 11. A control system toimplement such a method is depicted in FIG. 20.

In FIGS. 1-5, the following notations are used:

L_(l) denotes the l^(th) level out of L total levels;

At level 1: O_(ih) denotes the h^(th) orifice of the inlet circuit(O_(oh) is its counterpart for the outlet circuit);

Similarly, CP_(ih), represents the h^(th) channel portion of the inletcircuit, (CP_(oh) pertains to the outlet circuit). For example, CP_(i1)denotes the first channel portion of the inlet circuit, at level 1;

At level 2: O_(ihk) represents the k^(th) orifice arising from CP_(ih);CP_(ihk) denotes the corresponding channel portion;

At level 3: O_(ihkl) represents the l^(th) orifice arising fromCP_(ihk), CP_(ihkl) denotes the corresponding channel portion, etc.

The number of indices hkl . . . used to tag a particular orifice orchannel portion corresponds to the level that the orifice or channelbelongs to. For example, O_(ihk) belongs to level 2, while O_(ihkl)belongs to level 3.

Referring to FIGS. 1-5 in general and more particularly to FIGS. 1 and3, a chip module cooling device (or cooler) 25 as involved inembodiments includes two fluid circuits: an inlet fluid circuit i and anoutlet fluid circuit o. Each circuit includes an arrangement of orificesO_(i), O_(o) and channel portions CP_(i), CP_(o). The orifices are alsoreferred to as nozzles in some places below: they can indeed be givenvarious appropriate shapes such as injection nozzles. This arrangementcan be regarded as forming (or reflecting) a tree structure. An exampleof such a tree structure is depicted in FIG. 3, wherein: branchesrepresent the orifices O_(o), O_(o) and nodes represent the channelportions CP_(i), CP_(o).

As generally known in tree structures, a branch links a node to onechild node only; nodes sharing a same parent node are called siblings,or sibling nodes. Thus, channel portions corresponding to sibling nodesmay be called sibling channel portions.

Each fluid circuit extends through L levels (i.e., L₁ to L₃ in FIG. 1)of the tree structure. The concept underlying the present coolingdevices requires at least L≧3 levels. L can be larger, see e.g., FIG. 3.In FIG. 1, level L₄ could be regarded as an additional level of the treestructure. However, L₄ includes a modified orifice structure; it furtherincludes channel portions of a heat exchanger, which shall be describedlater.

The circuits connect to each other at (or after) a final level (i.e., alowest level of the tree structure), via channel portions correspondingto leaf nodes of the tree structure. The connection of the fluidcircuits can be realized directly via the final “leaf” channel portions,or not. The connection may for instance involve additional orifices orany sort of connecting structure (channels, slits, etc.) “after” theleaf channel portions in the tree structure. Examples are given below.The additional mechanism need not be reflected in the above treestructure. Fluid communication from the inlet to the outlet fluidcircuit is nonetheless enabled via a lowest level of the tree.

Now, for each of the two fluid circuits, the channel portionscorresponding to sibling nodes have to fulfill two conditions:

First, they are parallel to each other, i.e., the principal directions(or lines) of extension of sibling channel portions are parallel to eachother. Parallel is here to be understood according to Euclid'sdefinition of parallelism, i.e., it means strictly parallel and refersto two parallel distinct channel portions. In the example of FIG. 1, itcan be seen that sibling channel portions are parallel; this for exampleis the case:

At level 2 (L₂): for channel portions CP_(i11), CP_(i12), and CP_(i13)for inlet circuit i. The same occurs for the corresponding outletchannel portions CP_(o11), CP_(o12), and CP_(o13); or

At level 3 (L₃): for channel portions CP_(o131), CP_(o132), etc.;

Note that at level 1 (L₁), there is only one channel portion (CP_(i1) orCP_(o1)) per circuit (i or o), forming only one channel.

Second, channel portions corresponding to sibling nodes extend alongrespective directions, none of which is parallel to the direction ofextension of the channel portion corresponding to the parent node(compare e.g., L₃-channel portions to L₂-channel portions or L₂-channelportions to L₁-channel portions).

Provided that the directions do not intersect either (which shallimprove compactness in fine), it follows that, each of the channelportions corresponding to sibling nodes extends along a direction which,together with a direction of extension of their parent node, form a pairof skew lines. This condition could be fulfilled at a given level,preferably more, of the tree structure and for each of the two fluidcircuits. Siblings may span a plane parallel to the parent node of thesibling nodes. A sibling can thus be described as being “rotated”,preferably by 90° (as is the case in FIG. 1 or 3), with respect to theirparent channel portion. The extent of the rotation depends on thepattern drawn by the orifices, as to be explained in detail below.

Channel portions may advantageously fulfill the additional conditionsbelow:

Third, the channel portions corresponding to sibling nodes arepreferably strictly parallel to channel portions corresponding to agrandparent node of the sibling nodes, if any. This is notably the casein FIG. 1 for all L₃-channel portions (CP_(o131), CP_(o132), etc.) thatare parallel to CP_(o1) or CP_(i1) of level 1. It can be realized thatthis third condition allows for improved compactness, simplifies thedesign and thus eases the manufacture of the device, all the more ifL>3. However, this is not a strict condition (especially if L=3). Forexample, L₃-channel portions could extend not parallel to theirL₁-grand-parent channel portions, without critically impacting essentialproperties of the device. This could for instance be the case if otherconstraints (components, manufacture) oblige to shift grand-parentchannel portions from their ideal direction of extension.

Fourth, channel portions corresponding to sibling nodes preferably spana plane parallel to channel portions corresponding to a parent node.Again, this may improve compactness and/or simplify the design andmanufacture. This fourth condition is however not strict as the parentchannel portions could extend in a same plane as the sibling channelportions (though rotated with respect to the latter). In particular, inFIG. 1, it can be seen that:

Channel portions CP_(i11), CP_(i12), and CP_(i13) are open on an upperplane of component 211, which upper plane is (strictly) parallel to themain direction of extension of channel portion CP_(i1) (the parent nodeof CP_(i11), CP_(i12), and CP_(i13)).

However, the main direction of extension of CP_(i1) is close to or caneven be included in the average plane spanned by the main directions ofextension of CP_(i11), CP_(i12), and CP_(i13). Because there are onlyone inlet channel and one outlet channel at level 1, the latter cannonetheless be easily integrated in a same device block 251 as theirchild channel portions. Yet, because of the layer structure adopted inthe example of FIG. 1, channel portions of level 3 do not belong to thesame layer as the channel portions of level 2. Channel portionscorresponding to sibling nodes of level 3 now span a plane strictlyparallel to channel portions corresponding to a parent node. Thus, oneunderstands that sibling channel portions may advantageously span aplane parallel to their parent, subject to other constraints.

Finally, channel portions of the inlet circuit (for example CP_(i11),CP_(i12), and CP_(i13)) are parallel to and interdigitated with channelportions of the outlet circuit (for example CP_(o11), CP_(o12), andCP_(o13)). Interdigitation means an interlinking, evoking fingers of twohands locked together, as illustrated in FIG. 1 or FIG. 3. Owing to theconditions that the device already fulfills, Interdigitation involveschannel portions corresponding to a same level of the tree structure.

A similar arrangement is shown in FIG. 3. What FIG. 3 actually depictsis a 3D tree structure, i.e., a tree abstraction, representing anarrangement of orifices and channel portions. However, it should berealized that a cooling device may be embodied with a geometry ofchannels as depicted in FIG. 3. In FIG. 3, for each of the inlet/outletfluid circuits (i, o), channel portions corresponding to sibling nodesfulfill the same conditions as described earlier. Namely:

First, siblings are parallel to each other, as for example is the casefor: Channel portions CP_(i11) and siblings; the same occurs for theiroutlet counterparts (channel portions are not all referenced, forclarity); or Channel portions CP_(i111) and parallel siblings; andagain, at level 1, there is only one channel portion CP_(i1) for theinlet circuit (and similarly for the outlet circuit). Second, they arenot parallel to channel portions corresponding to a parent node of thesibling nodes (compare e.g., CP_(i111) to CP_(i11)); they are insteadrotated by 90°. Third, siblings are further parallel to channel portionscorresponding to a grandparent node of the sibling nodes. This isnotably the case for all channel portions of level 3 (CP_(i111) andsiblings, inlet circuit) that are parallel to their unique grand-parentchannel (CP_(i1), level 1, inlet circuit). Fourth, channel portionscorresponding to sibling nodes (e.g., CP_(i11) and siblings, inletcircuit) span a plane, which, in the embodiment of FIG. 3, is strictlyparallel to channel portions corresponding to a parent node (e.g.,CP_(i1), inlet circuit).

A structure such as described above allows for achieving a dense andhomogeneous arrangement of channels at the heat exchange level, i.e.,“after” the leaf level. In some cases at least, the third conditionabove further improves final compactness. The fourth condition may beomitted, depending on the number of grand-parents. Interdigitationresults in a homogeneous distribution of channels and allows forminimizing fluid trajectory. The fractal-like pattern that results fromchannel subdivisions and rotations makes it possible, notably, tooptimize heat exchange. In addition, particular implementations allowfor minimizing the required pumping power for the coolant flow. Detailedexamples are given below.

In addition, such a structure and its building principle are easilyscalable, which is advantageous for e.g., multichip photovoltaic cellsas the dimensions of the latter can substantially exceed typicalintegrated circuit (IC) chips.

Tests performed by the present inventors have shown that usual chipcooling devices (wherein fluid circuits can be seen as subdividing intoa single level of multiple nozzles/channels) can be successfully used tocool down classical IC chips, without unreasonable pumping effort.Scalability is therefore not an issue for cooling classical IC chips.Now, classical IC chip cooling devices are not suitably dimensioned formultichip photovoltaic cells. Should one nonetheless want to useclassical cooling devices for (larger) multichip photovoltaic devices,one may first be tempted to parallelize such classical cooling devices,owing to the dimensions of multichip photovoltaic devices compared tousual IC chips. However, experiments have shown that this isinappropriate, because some regions of the multichip photovoltaicdevices shall not be satisfactorily cooled, due to the inhomogeneouscooling obtained by the parallel cooling devices. Next, should one wantto scale a classical IC chip cooling device to typical multichipphotovoltaic device's dimensions (wherein dimensions are likelymultiplied by a factor >5 compared to a typical IC chip), another issuearises. In that case, present inventors have realized that scaledcooling devices require a (too) large pumping effort.

On the contrary, a cooling device comprising a multilevel andinterdigitated arrangement of orifices/channel portions as describedearlier is scalable, by construction. Such a building principle furtherallows for reaching a dense arrangement of channel portions at the leaflevel, owing to the successive rotations of channel portions. Dimensionsof cross-sections of both the channels and nozzles shall likely decreasefrom one level to the other, as the number of channel portions andnozzles increases from one level to the other. It can be realized thatthe height of the channels is not that critical: for instance, inembodiments, the height of the channels extends perpendicularly to thethickness of a layer wherein the channel is provided. However, the widthof the channel portions (in the cross-section, perpendicular to thein-channel flow direction) shall typically decrease. In other words, ifthe density of the channels is maximal at level n, the channel sectionsshall likely be larger at level n−1 than at level n. A structure asdescribed above allows for reducing the flow path to and within the heattransfer structure; it further allows for scalability while keeping amoderate pumping effort.

Typically, each of the two fluid circuits includes, at each level L_(l)(1≦l≦L−1):

-   -   N_(l) orifices (or nozzles), each leading to a respective        channel portion. An orifice typically branches in the middle of        the respective channel portion, except at edges of the device.        Other branching geometry can be contemplated, which however are        expected to be less efficient; and    -   N_(l) parallel channel portions. In turn, each of the N_(l)        channel portions shall enable fluid distribution to B_(l+1)        orifices of the next level L_(l+1), where B_(l+1) is a branching        factor, defined by B_(l+1)=N_(l+1)/N_(l). Successive        subdivisions of the channel circuits require B₂≧2 and B₃≧2; B₁        can be assumed to be equal to 1. For example, in FIG. 3:

O_(i1) leads to CP_(i1) (level 1, B₁=1);

CP_(i1) subdivides via O_(i11), O_(i12) and O_(i13) into respectivechannel portions (CP_(i11) and siblings, level 2, B₂=3);

Each of the L₂-channel portions (CP_(i11) and siblings) leads to fourchannel portions. For example, CP_(i11) leads to CP_(i111) (viaO_(i111)), as well as to three other parallel channel portions(siblings) via respective orifices; CP_(i12) leads to CP_(i121) as wellas to three other parallel channel portions (siblings), etc. Thus, atlevel 2: each channel portion of the inlet circuit enables fluiddistribution to B₃=4 inlet orifices (e.g., O_(i11k), k=1, 2, 3, 4) ofthe next level L₃. The same holds for channel portions of the outletfluid circuit.

In other words, the tree structure underlying each fluid circuit istypically balanced, as illustrated in FIG. 3, i.e., the branching factorB_(m+1) is preferably the same for each channel portion at a given levelL_(m), whereby both the design and the manufacture of the device aremade easier.

Next, the arrangement of orifices/channel portions can be designed suchthat each circuit has exactly the same geometry, which simplifies themanufacture and assembly of the device. Meanwhile, the arrangement canbe designed to optimize the fluid distribution at a leaf level, i.e., inthe vicinity of the heat exchanger. One possibility is to have, at agiven level L_(m) (2≦m≦L), the positions of orifices of one fluidcircuit correspond to a first set of discrete points of a first finitearray. In analogy with 2D crystallography, this first array may beregarded as generated by a set of discrete translations R, i.e., definedby R=n₁ a₁+n₂ a₂, where n₁ and n₂ are integers and a₁ and a₂ arelinearly independent vectors (as defined in linear algebra). Channelportions at level L_(m−1) extend along or parallel to a₁ and channelportions at levels L_(m) extend along or parallel to a₂. Finally, thepositions of orifices of the other fluid circuit may correspond tosecond set of discrete points of a second finite array, translated fromthe first array by a translation r defined by r=x₁ a₁+x₂ a₂, with 0<x₁<1and 0≦x₂<1. Preferably, on chooses x₁=x₂=½, which optimizes thehomogeneity of the fluid distribution at the level of the heat exchange.Choosing x₁ or x₂≠½ would instead induce heterogeneity in the set oftrajectories throughout the fluid structure and therewith would causeheterogeneous fluid distribution within the heat exchanger, resulting inheterogeneous cooling. Note that for m≦L−1, we have 0<x₁<1 and 0<x₂<1,while for m=L, we have 0≦x₁<1 and 0<x₂<1 or 0<x₁<1 and 0≦x₂<1. Also, asa consequence of the above arrangement, the N_(l) channel portions atlevel L_(l) are rotated with respect to channel portions of thenext/previous level, typically by an angle α=π/2 for a square lattice,as illustrated in FIG. 3.

Should the basis unit of the lattice differ (e.g., oblique lattice),then channel portions corresponding to child nodes of a given parentnode would be rotated by an angle α with respect to the parent channelportion and grand-child channel portions would preferably be rotated byan angle π−α, to be in phase with the parent.

For example, in FIG. 3, at level L₃, the positions of {O_(i111),O_(i121), O_(i112), . . . } map onto a first array, generated bytranslations R=n₁ a₁+n₂ a₂. Channel portions at level L₂ (e.g., CP_(i11)and siblings) extend along or parallel to a₁ and channel portions atlevels L₃ extend along or parallel to a₂. Finally, the positions oforifices of the other fluid circuit (not referenced for clarity)correspond to a second set of discrete points of a second array, at anylevel. L₁ to L₃ outlet orifices are translated from the first array byr=(a₁+a₂)/2. Next, in order to take account of edge effects, L₃-channelportions are modified: the leftmost inlet channel portions are reduced(compare CP_(i111) to CP_(i121)) and the corresponding orifices branchat one end thereof; the outlet structure is simply rotated with respectto the inlet circuit (π-rotation around O_(i1)) and is still shifted. Asa result, L₄ outlet orifices are translated from the first array byr=a₁/2 only, consistently with the fact that for m=L, the condition forx₁ and x₂ becomes 0≦x₁<1 and 0<x₂<1 or 0<x₁<1 and 0≦x₂<1, as notedabove. Such an arrangement has several advantages: (i) it makes itpossible for the inlet and outlet circuits to have exactly the samestructure (outlet circuit is simply rotated with respect to inletcircuit); (ii) it furthermore equalizes the fluid trajectories from onecircuit to the other at level 4 (the fluid path length between one inletorifice to the closest outlet orifice is |a₁|/2; and (iii) the twocircuits have the same footprint (square lattice).

Next, depending on the orifice arrangement, subsets of channel portionsmay rejoin to draw channel lines, at a given level (e.g., CP_(i111),CP_(i121) and CP_(i131) form one such subset at level 3 in FIG. 3), orat several levels. Typically, two adjoining channel portions in any suchsubset are cousins (e.g., CP_(i111) and CP_(i121)). Accordingly, it canbe concluded that, in this example, any two channel portions at anylevel are either strictly parallel (like CP_(i111) and CP_(i112)siblings) or extend along a same line (like CP_(i111) and CP_(i121)cousins). In that respect, since a line can be defined by a point and adirection vector and two lines can be defined as parallel if theirdirection vectors are, two identical lines are parallel according tothis definition, even if they are not according to Euclid's definition(where two parallel distinct lines are called strictly parallel). Thus,any two channel portions at any level are at least non-strictlyparallel.

Note that a design option such as discussed in the previous paragraphmight be implied by the positions of the orifices, in particular if thelatter map onto an array as discussed above. In all cases, this designoption substantially simplifies the geometry and manufacture of thecooling device, as subsets of channel portions extend along a samedirection. A given channel line shall include channel portions arrangedin-line, wherein fluid communication is possibly enabled from onechannel portion to another. Whether to do so shall actually depend onvarious parameters, flow rates, channel sections, etc. For example, eachof the fluid circuits i, o may include (at least in one level L_(l)thereof): N_(l) channel portions forming Nc_(l) strictly parallelchannel lines C_(i), C_(o), wherein each of the Nc_(l) channel linesincludes channel portions arranged in-line. In fact, at a given level,sibling channel portions are strictly parallel (e.g., FIG. 3, CP_(i111)and CP_(i112), level 3), but some of the channel portions that havedifferent parents (e.g., CP_(i111), CP_(i121) and CP_(i131)) may bearranged in-line, resulting in Nc_(l) parallel channels (Nc₃=4 at level3 in the example of FIG. 3). The channel portions arranged in-line arenot necessarily in fluid connection: one may for example have wallsbetween the channel portions arranged in-line or the channel portions.Note that one necessarily has N_(l), from the above definitions.

A particularly simple design is obtained by setting Nc_(l)=B_(l),whereby Nc_(l) parallel channel lines correspond to Nc_(l) parallellines of orifices, as illustrated in FIG. 3, level 3. Accordingly, eachof the fluid circuits may include N_(l) channel portions forming B_(l)strictly parallel channel lines. In that case, each channel lineincludes B_(l−1) channel portions arranged in-line (and this, possiblyat each level L_(l)). Again, channel portions in a given channel linemay be connected to enable fluid communication from one channel portionto another. Now, one channel line may include a unique channel portion.For example, at level 1, one has C_(i1)=CP_(i1), assuming B₀=1 in thatcase; at level 2, one has C_(i11)=CP_(i11), etc., since B₁=1. However,at level 3, there are Nc₃=B₃=4 parallel channel lines (for each fluidcircuit), which lines correspond to respective parallel lines oforifices and include, each, 3 orifices and 3 respective channel portions(B₂=3).

In addition, it is desirable to further improve the compactness of thearrangement, to minimize the fluid trajectories. To that aim, Nc_(l)strictly parallel channel lines C_(i) of the inlet fluid circuit mayadvantageously be interdigitated with Nc_(l) strictly parallel channellines C_(o) of the outlet fluid circuit, at a given level L_(m) (1≦m≦L).Accordingly, each channel line of the inlet fluid circuit results to beparallel to each channel line of the outlet fluid circuit at that levelL_(m). Interdigitation of channel lines can actually be provided atseveral levels, and more preferably at each level where channel portionscan form channel lines), to increase compactness. In that respect, itshould be borne in mind that FIGS. 1 and 3 depict simple examples, butadditional levels (and layers) of channel portions may actually becontemplated.

Next, a specific pattern of channel portions shall be discussed inreference to FIG. 1 (enlarged “B” area) and FIG. 2 (focusing on thespecific pattern shown in the enlarged “B” area, designed for sublayersL₃₂ of the device of FIG. 1). Namely, at a given level L_(m) and foreach of the fluid circuits, at least some of the N_(m) channel portionsmay be designed to have a non-constant cross-section. As seen in FIG. 2,inlet and outlet channel portions can be suitably shifted (i.e.,interdigitated) to maintain a compact arrangement (compare e.g.,CP_(i124) to CP_(o124)). More specifically, the channel portions may,each, include an enlarged area vis-à-vis a respective one of the N_(m)orifices, to improve fluid distribution from/to orifices of therespective channel portions (at a given level L_(m)).

Additional design options can be contemplated, which take account ofedge effects. For example, at a given level L_(m) (e.g., L₃ in FIG. 1)two sets of orifices (e.g., O_(i11k) and O_(o13k), k=1, 2, . . . ), eachcomprising B_(m) orifices, are arranged in correspondence withrespective outermost channels (e.g., CP_(i11) and CP_(o13)) of aprevious level L_(m−1). Then, each of the B_(m) orifices of the two setsand/or each of their respective channel portions may have reduceddimensions along a particular direction of extension of the channels atlevel L_(m) (i.e., direction x in FIG. 1).

The cooling device may further include a heat transfer structure 24, inaddition to a manifold system, to supply and drain liquid to and fromthe heat transfer structure, as illustrated in FIG. 1 and FIG. 4. Invariants, the heat transfer structure 24 could be first integrated to aphotovoltaic module, and later be connected to the cooling device. Inall cases, the heat transfer structure 24 can be configured to connectone of the fluid circuits to the other. The heat transfer structurepreferably includes silicon, and is more preferably entirely made ofsilicon, for reasons that will be discussed later.

The heat transfer structure may for instance include heat transferchannel portions (e.g., CP_(t1311), CP_(t1312) in FIG. 1, enlarged area“D”). Each of the transfer channel portions connects at least onechannel portion (e.g., CP_(i131) in FIG. 1) corresponding to a leaf nodeof the inlet fluid circuit to one channel portion (e.g., CP_(o131) inFIG. 1) corresponding to a leaf node of the outlet fluid circuit.

Preferably, each heat transfer channel portion extends along a directionrotated with respect to a direction of extension of the channel portionsthat it connects, following the same principle as already discussed inrespect of the tree-structured channel portions of the cooling device.

Similarly, heat transfer channel portions may connect the lowest-levelchannel portions via slits (e.g., S_(i131) and S_(o131) in FIG. 1),following the same principle as for orifices nozzles discussed thus far,except that the dimensions typically involved at the level of the heattransfer structure make it preferable to have a slit instead of a densein-line arrangement of orifices, for manufacturability reasons. Yet, aslit can be seen as the asymptotic limit of such an arrangement. In thatsense, the heat transfer structure can be regarded as forming orcompleting an additional level of the tree structure underlying eachfluid circuit, e.g., level 4 in FIG. 3.

Next, the cumulated width of all orifices (in cross-sectional areas) ofone of the levels is preferably kept substantially equal (e.g., to ±15%)to the cumulated width in cross-sectional area of all orifices ofanother, e.g., a contiguous level (and preferably of all of the otherlevels), in order to limit the pumping effort.

In an example, at a given level L_(m):

the length of a channel portion (not at an edge) isL_(m)=(L₁−W_(min))/B_(m−1); and the width of a channel portion isW_(m)=L_(m−1)/B_(m)/2−W_(min),

wherein W_(m) is a width of the channel portions at level m and W_(min)is a minimal wall thickness. The above dimensions are valid if W_(m) isthe same for inlet and outlet channel portions and if it is constant foreach portion, subject to edge effects.

The height of the channels may for instance be independent from onelevel to each other. Assuming that all levels should have the samefootprint, the relationship between the lateral dimensions of thechannels from one level to the next shall notably depend on thebranching factor.

In terms of manufacturability, it may be advantageous to have one ormore levels embodied, each, as superimposed sub-layers (e.g., sL₃₁ andsL₃₂ for level 3 in FIG. 1). In FIG. 1: a first sub-layer sL₃₁ includesorifices, whereas the second sub-layer sL₃₂ includes channel portions.Both the orifices and channel portions can be machined as through holesin their respective sub-layers, which makes the manufacture processeasier. Superimposed layers may be made of different materials, ifnecessary, since the different dimensions and shapes of the channelportions vs. orifices may more easily be processed using differentmaterials.

A cooling device such as described above is advantageously used togetherwith a photovoltaic receiver 20, such as depicted in FIG. 8 or 9. Thisreceiver may include a photovoltaic module 21, such as depicted in FIG.4 or 5. The receiver shall further include a heat circuit portion 71 a(FIG. 8, 9), connected to the photovoltaic module and the cooling device25, the latter forming part of the heat circuit portion 71 a.

Preferably, the above cooling device is used together with aphotovoltaic thermal hybrid solar receiver 20, such as illustrated inFIG. 8 or 9. The latter further includes thermal collector 22, distinctfrom the photovoltaic module 21 of the receiver. In that case, the heatcircuit portion 71 a is a first heat circuit portion 71 a, distinct froma second heat circuit portion 72 a, that connects to the thermalcollector. Such a photovoltaic thermal hybrid solar receiver 20 shall bedescribed in detail below.

Cooling Devices: Specific Implementation Details

The cooling device is preferably designed to allow for cooling the cellpackage with elevated temperatures of the coolant while keeping the cellat a moderate temperature (<100° C.). This way the collected thermalenergy is of high value due to its elevated temperature level.

For this purpose the cooling device is preferably designed to haveminimal thermal resistance between the PV cells and the cooling fluid. Acooling device such as described above may provide thermal resistance ofless 0.11 cm²K/W. Assuming the PV cell is connected to the coolingdevice by a solder interface the total thermal resistance from the PVcell surface to the liquid coolant is around 0.17 cm²K/W. This allowscooling for heat flux densities of more than 400 W/cm² while keeping thecell at less than 100° C. (assuming the fluid inlet temperature is 30°C.).

The cooler can be optimized to operate at low pumping powers, therebyreducing the energy needed to operate the system. The above solutionsallow a homogenous cooling performance over an extended area (ΔT<±0.2 K)that can be easily scaled.

Reliability of the package may also be considered. A solution usingsilicon as substrate material allows a good thermal coefficient ofexpansion match between the PV cells (typically germanium) and thecooler, which reduces stress on the cells. Use of silicon further allowsfor using MEMS processes to structure cooler surface and implementsensing elements in the cooler (temperature, radiation, pressure . . .).

Minimizing pumping power while maximizing temperature homogeneity acrossthe cooler surface can be both achieved with an efficient manifold suchas described above, i.e., a hierarchical fluid distribution/collectionsystem with two main paths (fluid inlet and outlet).

A layer-wise implementation of distribution channels (manifold) andinjection orifices (nozzles) allows for: using different materials andfabrication methods to cover the broad range of structure dimensions(e.g., from 20 μm to 20 mm or more); using different materials, which inturn allows for achieving low thermo-mechanical stress in the coolinglayer, increasing the lifetime of the package, and scalability.

The cooler package is preferably fabricated using MEMS technology,taking advantage of definition and processing of microstructures, batchprocessing, bonding techniques, integration of sensing elements, etc.

In reference to FIG. 1, 4 or 5, this package typically includes a layer21, on top, comprising PV cells 211, forming a multichip module 212, thePV cells connected by electrical interconnects (see below); bypasselectrodes 213; and an electrical layer (214), to connect the bottomelectrodes of the PV cells. Layer 21 may further contain: a sensor layerwith a network of resistive temperature devices to map the temperatureover the entire package right at the bottom of the PV cell (not shown);an insulation layer, to insulate the sensor layer to electrical layer(not shown). These layers are typically processed using thin filmdeposition techniques as well as galvanic processes. Solders can beapplied by a galvanic process too or any conventional process likescreen printing.

In the cooling sub-layers, micro channels can be fabricated by DRIE toenhance heat removal. These channels can be also fabricated usingmultiple dicing saws. In an orifice sub-layer (e.g., sL₃₁ in FIG. 1):orifices can be fabricated by DRIE. Die casting and other massproduction processes can also be used to fabricate such a sub-layer.

A multichip module package including a cooling device as described abovemay include high efficiency triple junction solar cells (or “3JPV”,commercially available) soldered onto a substrate with a minimaldistance between each other; a cooler package (or heat sink) having amicro machined silicon wafer 24, i.e., a heat exchanger and carrier ofelectrical network, with a micro machined heat transfer structure on thebottom side, comprising channels (such as CP_(t1311) in FIG. 1 or 4);integrated temperature sensors; an electrical network consisting ofelectrically conductive pads (214) which connect to the bottom electrodeof a PV cell; a manifold system, for fluid distribution and collection,with one substrate combining orifice sub-layer sL₄₁ and manifoldsub-layer sL₃₂ and one substrate with orifice sub-layer sL₃₁. With sucha (specific) design, two sub-layers can be combined in a singlesubstrate to take advantage of the specific process of double side DRIE.Doing so the number of components and interfaces can be reduced. Ingeneral layers should be combined if the process and the design allow,in order to reduce fabrication costs.

Electrical interconnects (including conductive pad 214, connection 216,etc.) which connect a top electrode of one cell to a top electrode ofanother cell in case of a parallel connection or which connect a topelectrode of one cell to a electrically conductive pad 214 which isagain connected to the bottom electrode of another cell in case of aserial connection (see below, 300 μm wire bond, soldered or welded Curibbon or lead frame). A carrier 251 for mechanical support andinterface to larger system includes a manifold layer (embodying bothlevels L₁ and L₂), made of polymer, metal, composite materials, etc.

In reference to FIG. 5, a multichip module receiver package shalltypically include, in addition to components described earlier, a shield215 to protect components not meant to be exposed to radiation. Inaddition, the shield encapsulates the PV cell package to protect againstdust, humidity, etc. The shield further includes a cover window 215 athat can be used to filter radiation, if needed, see section 2.2. Shieldwalls 215 b can be used as secondary reflectors to homogenize incomingradiation. The shield has a heat recovery system that can be coupled tothe cooling loop, in series, or to a separate heat circuit, as describedin detail below

Photovoltaic Thermal Hybrid Solar Receivers

In reference to FIGS. 6-10, novel photovoltaic thermal hybrid solarreceivers 20 are now described. In each case, the hybrid receivers firstinclude a thermal collector 22. The latter extends in a first plane 220,which plane typically is a main plane of extension of the thermalcollector, i.e., the plane onto which radiation can be received andcollected. The location of the first plane is preferably taken at thelevel of the average plane of the thermal collection panel of thecollector, as depicted in FIG. 8 or 9. This thermal plane can thereforealso be referred to as a ‘shield’, as done in some places below. Inaddition, the thermal collector includes an aperture 68.

The receivers 20 further include a photovoltaic module 21. Such a moduleis designed for delivering an electrical output power P_(O), inoperation, as known per se. The module notably includes a photo-activearea 212 that extends in a second plane 210. The latter typically is amain plane of extension of the area 212, e.g., the average plane of thephoto-active pane of the module. It is furthermore preferably parallelto the first plane, for both simplicity and efficiency reasons, thoughparallelism is not a requirement at all. In all cases the second plane210 is located at a distance 232 (see FIG. 8 or 9) of the first plane220 and the area 212 is located vis-à-vis the aperture 68. Theprojection of the aperture, i.e., perpendicularly to the second plane210, corresponds to the photo-active area (or essentially corresponds toit). Here, ‘essentially’ means that the photo-active area may represent80 to 100% of the projected area of the aperture.

The above design, wherein plane 210 is distant from the plane 220 andarea 212 is set vis-à-vis aperture 68, allows for easily varying a ratioof radiation exposure of the photovoltaic module 21 to the thermalcollector 22, e.g., by simply translating the device perpendicularly toplane 210, with respect to a radiation focus point or plane. This deviceaccordingly makes it possible to rapidly “switch” from PV power deliveryto thermal power storage.

Another advantage is that: when the light beam is defocused, the PVelectrical output becomes smaller but the thermal output on the fronttarget is larger. A benefit can therefore follows even with amisalignment. Thus, a less accurate tracker and a higher maximal opticalconcentration with a lower cost mirror can be reached.

In addition, the thermal collector and the photovoltaic module may beconfigured to protect peripheral regions of the photovoltaic module fromradiation hitting the thermal collector. Namely, the thermal collectormay be designed to protect peripheral regions of the main plane of thephotovoltaic module and at least partly shields radiation received froma light source at the photovoltaic module, e.g., to protect passivediodes or passive components in the photovoltaic module.

Preferably, a hybrid receiver further includes a first heat circuitportion (ref. 71 a in FIG. 8 or 9), thermally connected to thephotovoltaic module (at the back thereof), and a second heat circuitportion (72 a) thermally connected to the thermal collector. The circuitportions can be connected to respective heat circuit portions, typicallyclosed-loop, as to be discussed below. The circuit portions 71 a and 72b can be thermally insulated from each other, if necessary. Portion 71 aor 72 a, or both portions 71 a and 72 a could for instance be embodiedas a cooling device such as described earlier, in section 2.1, see e.g.,ref. 25 in FIG. 1 or 4.

Typically, the first circuit portion 71 a is inserted in a first heatcircuit 71, configured to cool the PV receiver, and the second circuitportion 72 a is inserted in a second circuit 72, independent from thefirst circuit, and connecting in turn to a thermal storage, to serve apurpose described in the next section. In variants, the first portion 71a and the second portion 72 a may be thermally connected, in series, ina same heat circuit, subject to additional constraints to be discussedlater. For completeness, FIGS. 8, 9 show inlet/outlet circuit sections71 i, 71 o, 72 i, 72 o, of respective circuits 71, 72.

The distance 232, as well as the distance 231 between the area 212 and alower end 68 a of aperture 68 both depend on a number of design andsystem options, which are discussed later in details (desiredinsulation, circuitry dimensions, presence of a homogenizer, a filter, aconcentrator and characteristics thereof, translational speed anddesired reactivity of the system, etc.).

For instance, the end 68 a of the aperture 68 that is the closest to thephoto-active area 212 is preferably kept at a (small) distance from thisarea 212, as illustrated in FIG. 8, to ensure thermal insulation.Typically, this end of the aperture 68 is located at a distance largerthan or equal to 0.2 mm, which may already suffice to insulate thethermal collector from the PV receiver, as tests have demonstrated (aircan be used as insulating medium). However, depending on the PV modulesize and cooling circuit temperature used, this distance may need to belarger than or equal to 0.5 mm, and/or other insulating material may beused. On the other hand, this distance is preferably smaller than orequal to 3.0 mm. Indeed, it can be realized that this gap needs to besmall enough so that light cannot “escape”. Namely, light exiting theaperture has a defined angle, the above distance is therefore designedsmall enough so that outcoming rays shall not hit the periphery of theactive area. Depending on other device specifications, this distance maymore preferably be smaller than or equal to 2.0 mm, and even morepreferably 1.0 mm. The accompanying figures are obviously not to scale,at least not in respect of every feature shown.

Now, it can be realized that, since (i) minimal thermal circuit sectionstypically have a diameter of 5 mm, and (ii) the end 68 a is located at adistance larger than 0.2 mm, then the minimal distance 232 need belarger than 2.7 mm. Instead, using a 6 mm circuit diameter would bringthis value to 3.2 mm. This minimal distance is increased if, inaddition, an intermediate homogenizer is used (e.g., at least 10 mm,optimally 60 mm long for an aperture of approximately 35×35 mm and anlight incidence angle of 53°, the rim angle of the parabolic dish). Moregenerally, if no homogenizer is provided, the minimal distance 232, FIG.8, is determined by the dimensions of the thermal collector (thatincludes thermal circuit 72 a, panels, etc.).

Note that, at variance to FIG. 8 or 9, the thermal collector 22 mayinclude a tapered aperture section, i.e., with a non-constant crosssection. In that case, the end 68 a of the aperture 68 would correspondto a smallest cross sectional area of the non-constant cross section.

As evoked earlier, the thermal collector may further include one or moreminor elements 74 (see FIG. 6, 7 or 9), for example a light homogenizeror, more generally, optics, i.e., secondary optics (beyond aconcentrator), in an intermediate section 75 between the first plane 220and the second plane 210. Such mirror elements can be configured tospecifically reflect incoming light 90 a-c and distribute reflectedlight 90 b-c onto the photo-active area 212, as illustrated in FIG. 9.For example, minor elements may be configured to homogenize and/orfurther concentrate reflected radiation 90 b-c onto area 212. To thataim, simple possibilities consist of having at least three or fourmirror elements 74, forming a closed hollow section 75, as depicted inFIG. 6, 7, or 9. Yet, a single tubular minor could be used.

Advantageously, the one or more minor elements 74 are thermallyconnected to the second heat circuit portion 72 a, such as to benefit toa corresponding heat circuit. In that case, optimal results shall beobtained if a part, at least, of the circuit portion 72 a is coiledaround the minor elements, as shown in FIG. 9 or 10. The neededcircuitry can for instance be suitably molded or arranged in aninsulating body, as better seen in FIG. 7, wherein sections 72 a 1-7 ofthe second heat circuit portion are visible.

Interestingly, the thermal collector may further include a bandpassfilter 76 (see FIG. 7 or 9), e.g., at the level of an upper end of theaperture 68 and fit within the aperture, to specifically select abandwidth where conversion efficiency of the PV cells is optimal. Apassband which is optimal for purposes described later is 350-1500 nm,i.e., it corresponds to the spectrum where preferred PV cells have aconversion efficiency larger than 80%. Preferred PV cells are typicallymulti junction solar cells, e.g., from Boing Spectrolab, Emcore, AzurSpace amongst others.

Advantageously, the filter can further be designed to thermally absorbradiation wavelengths outside the passband, i.e., to benefit again to aheat circuit, preferably the second heat circuit 72, in form of highergrade thermal energy.

In that respect, the filter may include a hollow cavity filled with acooling fluid 77 (see FIG. 7), in fluid communication with a heatcircuit, e.g., circuit 72. Other options are discussed later.

Next, hybrid receivers 20 such as described above can advantageous beused in an apparatus 10 such as depicted in FIG. 10 (or moreschematically in FIG. 12 or 13). Such an apparatus shall further includea concentrator 27. The latter is designed and configurable toconcentrate radiation towards an optical focus 80, as known per se. Theoptical focus 80 is a region of maximal intensity of concentrated light,e.g., essentially located to small volume or confined close to a plane,e.g., plane 80, depending on actual implementations.

The apparatus (or the concentrator device itself) further includespositioning mechanism 27 a, 27 b, 30, which can have various purposes.In that respect, the receiver and/or the concentrator can be movablymounted in the apparatus via the positioning mechanism.

For example, the positioning mechanism may be configured to change aratio of intensity of radiation 90 b,c received at the photovoltaicmodule to intensity of radiation 90 a received at the thermal collector.Because of their relative dimensions, it shall likely be simpler to makethe hybrid receiver movably mounted in the apparatus 10 via positioningmechanism 30 rather than the concentrator. The receiver can further bemovable with respect to the optical focus 80. Accordingly, the receiverand/or the concentrator are movable (e.g., along bi-directional axis 84)by the positioning mechanism from a position where the photovoltaicmodule 21 is in the optical focus 80 to a position where the thermalcollector 22 is in the optical focus.

Changing the ratio of intensity evoked just above is accordingly veryeasily obtained, e.g., via a simple translation of the receiver and/orthe concentrator. In this regard, the positioning mechanism may simplybe embodied as one of: a linear actuator, such as a rack and pinion; ora vehicle, such as a wheeled vehicle, a tracked vehicle, or a railedvehicle, for example comprising a trolley, a bogie, etc. more generally,the positioning mechanism 30 preferably enables bidirectional motionalong an axis 84 perpendicular to second plane 210. The mechanism 30 ispreferably specifically dedicated to the task of changing the aboveratio, and possibly to that task only. Usual tracking systems do notenable suitable bidirectional motion along axis 84, in operation.Indeed, in prior systems, the receiver's position is refined duringsetup but it is then fixed (definitively) for the life of the system forstandard systems.

Now, the concentrator 27 or one or more elements 271 thereof may furtherbe movably mounted in the apparatus via other positioning mechanism 27a, 27 b, as schematically depicted in FIGS. 10, 12, and 13.

FIGS. 12-13, which are simplified representations of two hybrid systems,illustrate the variation of the spot geometry at the receiver. In eachcase, the upper drawing represents a configuration for which the spot isfocused at the receiver plane, while the spot is defocused in the lowerdrawing. In addition, in FIG. 12, a classical parabolic concentrator(minor) 27 is used, while in FIG. 13, the concentrator includes aplurality of mirrors 271, which can be actuated by respectivepositioning mechanism 27 b, to change the spot geometry at a receiverplane (210 or 220, in FIG. 8-9).

As schematically illustrated, the spot geometry at a receiver plane canbe changed by:

FIG. 12: displacement of the receiver along the optical axis 84, e.g.,in a rotational symmetric parabolic concentrator, should a homogenizerbe involved or not; and/or

FIG. 13: changing the shape of the primary concentrator, for example bytilting of one or more (flat) elements 271 of a faceted minor.

In addition, one may defocus the spot by changing the curvature of themain mirror or the one of secondary optics in a folded beam arrangement.

As touched above, to move the receiver module 20 out of focus, thereceiver can be mounted on a movable stage. The stage can be actuated bya shaft and a stepper motor that are themselves mounted in a fixposition in reference to the focal plane of the concentrator system.This adjustable receiver positioning unit represents a control element30, symbolically represented by reference 30 in FIG. 10. Alternativelythe stage with the receiver can be moved using a hydraulic or pneumaticactuated piston, etc.

FIG. 16 shows typical cross sections of the intensity distribution(normalized intensity) at the PV receiver module plane (ref. 220 in FIG.8-9), when using a rotational symmetric parabolic primary concentrator,for a receiver module displaced along the optical axis of the system.The x-axis represents a distance r (mm) along a section passing throughthe aperture, where r=0 corresponds to a center of the aperture(typically a symmetry center). The darker gray box corresponds to theaperture, while the lighter gray boxes denotes the shield, i.e., thethermal panel of the collector 22 extending parallel 220 to the receiverPV module plane 220. As indicated by the various curves represented inFIG. 16, a light beam can be focused such that the radiation intensitydistributes mostly or essentially within a zone corresponding to theaperture (this intensity shall accordingly be converted to electricalpower thanks to the PV cells).

Defocusing the spot (or altering the mirror shape/elements) results inwidening the intensity profile, such that radiation becomes essentiallycollected at the shield.

In that respect, the shield 22 a (FIGS. 6-9) is preferably madesubstantially larger than the aperture 68. Typically, the aperture'sdimensions (e.g., between 10×10 and 30×30 mm) reflect that of thePV-MCM, while the overall shield dimension can reach 200×200 mm or more(e.g., 500×500 mm is possible).

FIG. 17 shows the total irradiance (normalized power) captured by thethermal collector (dotted curve) and the PV receiver (full line) whiledisplacing the element along the optical axis (distance d (mm) inabscissa) towards the primary concentrator. Typically, ˜30% of the solarradiation reaching the PVT receiver can be converted to electricalenergy while the remaining 70% can be captured as heat, which togetherwith the irradiance captured by the thermal collector contributes to astorage system. The design point of the system is preferably set to bebetween 90-20% of the load on the PVT receiver.

A number of conceptual variants can be contemplated. For instance, thethermal collector may have a conical shape. The thermal collector andthe homogenizer could be one and a same element, provided with a suitedshape to both collect solar radiation and distribute/concentratereflected light as appropriate onto the PV receiver. When using a flatfacetted mirror concentrator (as in FIG. 13), some of the facets couldbe fixed, others could be moved. Facets of the primary mirror can betilted to redirect light on the periphery of the receiver 20, where thethermal receiver panel is placed.

Additional variants may include light cones mounted directly on the PVchips with cooling (high temperature) that eliminate inactive surfaceson 3JPV chip array. Such cones are arranged such as to redirect thatlight that would otherwise hit contact pads of the solar cells and thegap between them. Light is redirected to the photoactive area, therebyincreasing the electrical efficiency of the system. A front electrodegrid with reflective surfaces may prevent shading of sensitive PVsurface. Antireflection surfaces using, e.g., moth eye patterns may becombined with front electrode grating that contributes to the wavelengthfiltering function by reflecting UV/blue light back to the homogenizer,to serve the more general functions of adsorption enhancement andfiltering, as described earlier. Switchable absorbers, depending onhumidity (large humidity and early morning/late evening may increase redshift and underload blue diode. Additional red absorbers may also beincluded.

The various features recited above, in respect of hybrid receivers, canbe advantageously combined, in several manners. For example, exergeticrecovery can be optimized by having a separate cooling loop 71 for themultichip receiver cooling 25 and for the homogenizer and shield cooling72. As explained, electrical output can be controlled by moving theassembly along the optical axis closer to the minor and away from thefocal plane. Exergy optimization can further use a wavelength selectivereflective filter to avoid exposure of the PV chips, e.g., a multichipmodule (or MCM) triple junction chips with light they cannot convert(UV, and far IR). The inactive area between the chips is advantageouslyreduced by having triangular reflectors placed on the front electrodesand the connection mesh (not shown for clarity).

A dispatched delivery scenario of electrical power by a CPVT system ascontemplated herein can for example be briefly described, in referenceto FIG. 18. FIG. 18 shows three curves, representing:

Full line: the morning power demand peak and the evening demand peak;

Dotted (gauss-like curve): a typical PV 2 hour design power, having amaximum around 13:00;

Short-dashed: a typical CPV 6 hours design power; and

Dash: an 8-9 hour design power, as can be achieved thanks to embodimentsof the invention. An 8-9 hour design power can indeed be achieved, i.e.,output power can now be maintained over 8-9 hours instead of just 2hours like for flat PV. In particular, the hybrid receiver can be movedout of the focal plane to reduce optical intensity, as explainedearlier. A feedback loop can move the receiver back to the focal planeto compensate for temporary irradiation loss (e.g., light clouds) or tomeet higher power output demand, as to be explained in more details inthe next section. The excess energy is harvested as heat, thanks to thethermal collector and associated circuit and used to bridge the morningand evening peak demands, e.g., using a Rankin engine with stored hot(and pressurized) water (e.g., 150° C.). Depending on the actual size ofthe thermal collector, this temperature cannot be too large, otherwisethis would lead to radiative losses from the large area thermalcollector.

More details as to operation methods and system description shall begiven in the next section.

Photovoltaic Thermal Hybrid Systems and Methods of Operation Thereof.

The present section focuses on methods to operate photovoltaic thermalhybrid systems. An example of hybrid system 10 is shown in FIG. 10. Somecomponents of or variants to this system are depicted in FIGS. 1-9,12-15, and 19-20.

Referring to FIGS. 1-20 in general and in particular to FIG. 11, themethods generally rely on a system 10 comprising: a hybrid solarreceiver 20 such as described in section 2.2, i.e., wherein the receiverincludes a photovoltaic module 21, operatively coupled to the system 10to deliver an electrical output power P_(O), e.g., for a power user; anda thermal collector 22 such as described in section 2.2 too.Importantly, for the purpose of implementing methods as describedherein, the collector must be distinct (e.g., thermally insulated) fromthe photovoltaic module. In addition, the photovoltaic module and/or thethermal collector are/is movably mounted in the system (e.g., on astage).

The system further includes a collector thermal storage 42. As discussedearlier too, the latter is thermally connected to the thermal collector22, typically via a closed-loop heat circuit 72, such that heatcollected at the thermal collector can be stored in the storage 42. Inthis application, two components “thermally connected” means the same astwo components “thermally coupled”, i.e., heat can be exchanged from onecomponent to the other. Finally, system 10 includes positioningmechanism 30, which are adapted to move the photovoltaic module and/orthe thermal collector.

Next, the operation methods include a step of instructing (FIG. 11, stepS30) the positioning mechanism 30 to move the photovoltaic module 21and/or the thermal collector 22 to change a radiation intensity ratio.The ratio compares intensity of radiation received (FIG. 11, step S10)at PV module 21 to intensity received (S 10) at the collector 22. Oneunderstands that such methods can take advantage of devices such asdescribed herein.

Whether to instruct the positioning mechanism 30 to move thephotovoltaic module 21 and/or the thermal collector 22 is typicallydecided at a control system/unit 100 such as depicted in FIG. 20. Thiscontrol system/unit shall be described in detail in the next section.Note that decision S30 can be based on a power demand as calculated,predicted, etc. but could also be based on thermal demand (at leastpartly). A power demand is the power needed from the grid at aparticular time, e.g. noon peak or evening peak.

For instance, referring in particular to FIG. 11, data indicative of anelectrical power demand P_(D) may be received at a step S80. DecisionS30 may then be carried out based on a comparison (steps S20, S22) ofthe PV output power P_(O) (e.g., as delivered by the PV module) with thepower demand.

Note that in typical applications, power demand is AC whereas the outputpower is DC. Thus, the system 10 shall typically include an inverter 28,see FIG. 10, through which power is processed before delivery to poweruser. In case, indirect comparison might be needed (AC to DC), dependingon the system's logic 100. In general, P_(D) is always AC power. Since aDC/AC conversion ratio or calibration curve is usually known, it caneasily be integrated in the feedback loop. Conversion may change withloading (e.g., 98% at 100% load and 96% at 50% load) but an exactcalibration curve is usually available.

In particular, decision S30 may be made to suitably move the PV moduleand/or collector to decrease the radiation intensity ratio if comparisonS20 indicates that the output power P_(O) is larger than the powerdemand P_(D). Indeed, if P_(O) is larger than P_(D), it can be realizedthat leaving the configuration of the PV module vs. collector unchangedis sub-optimal. On the contrary, with a receiver 20 such as describedabove, the configuration of the receiver 20 can be altered to favorthermal collection instead of electrical power conversion.

Now, it can be instructed (step S24) to deliver the output power P_(O)generated by the PV module 21 to a power user, to meet the power demandP_(D) if P_(O) matches the power demand P_(D), based on the comparisoncarried out at steps S20, S22. In FIG. 11, P_(d) denotes the actuallydispatched power (step S24, S57 or S52). Complete description of FIG. 11shall be given later.

Typically, such comparisons S20, S22 are subject to a tolerance, whichdepends on the system capacity, reactivity, etc. This tolerance can beadjusted empirically, e.g., based on trial-and-error process. Also, hereagain, consistent power values are compared (e.g., AC to AC).

Additional components may be provided in the system 10 to furtheroptimize it. For instance, system 10 may further include a heat engine62, as depicted in FIGS. 14-15. The heat engine 62 is thermallyconnected to the collector thermal storage 42.

In that case, present methods may further include steps of instructing(FIG. 11, steps S50, S56) the heat engine 62 to start a process ofthermal-to-electrical conversion, to convert heat stored in thecollector thermal storage 42. Whether to do so is typically decidedbased on comparisons S20, S22, i.e., if it turns out that P_(O) is lowerthan the power demand P_(D).

Note that the heat engine 62 can be any kind of thermal-to-electricalconverter suited for the present purposes, e.g., to run a Rankine cycle,preferably an organic Rankine cycle (ORC), which uses an organic fluidsuch as n-pentane or toluene in place of water and steam. This allowsfor using lower-temperature heat sources, which typically operate ataround 70-90° C., but works still better at higher temperatures such as120-150° C. as presently contemplated. Suitable fluids can be chosenamong Hydrochlorofluorocarbons (HCFC), Chlorofluorocarbons (CFC),Perfluorocarbons (PFC), Siloxanes, Alcohols, Aldehydes, Ethers,Hydrofluoroethers (HFE), Amines, Fluids mixtures (zeotropic andazeotropic), Inorganic fluids. Examples are: R245fa, R123, n-butane,n-pentane and R1234yf, Solkatherm, R134a, R600, carbon dioxide, R152a,R600a, R290, etc. A comparison of the critical temperatures of thefluids vs. optimal operation conditions of systems as contemplatedherein allows for refining the choice. In particular, experimentsconducted in the context of the present invention have shown that fluidsR134a, followed by R152a, R600, R600a and R290 are most suitable fluidsfor low-temperature applications driven by heat source temperature below90° C. In variants, a thermoelectric generator is relied upon, whichconverts heat to electrical power without working fluid and movingparts. Yet, thermoelectric generators currently have lower conversionefficiency for kW to MW sized converters.

A control system (FIG. 20, ref. 100) with feedback loop is used to adaptthe electrical power output to the actual demand required, e.g., by agrid control station. FIG. 11 shows an example of a main control processfor a dispachable power mode. In this example, the generated electricalpower is the main control variable and is adapted to the demand usingthe receiver positioning system. The positioning response is in therange of seconds, while the start of a Rankine cycle can be predictedand therefore kept with the same response time.

Even more valuable than dispatched power is the function of gridservices. A photovoltaic unit with motorized receivers can take thisfunction when a feedback loop is closed between the phase angle Φ in thegrid (indicating the load situation) and the position of the receiver.

The smaller the angle Φ the more is the receiver moved away from thefocus; the larger the angle Φ the closer the receiver is moved to thereceiver. Most valuable are grid services that can react very fast i.e.within seconds, a thing that can be achieved thanks to embodiments ofthe present invention.

In this respect, an inverter can switch off an input current in a matterof milliseconds, e.g., in a situation where the grid fails (lightning orphysical damage). In this situation the receivers 20 can be moved to theminimum power position within a few seconds; power can thus bedissipated in open circuit voltage mode. The generated charges flow backin the PV diodes, adding thermal load to the microchannel cooler.Accordingly, no damage to the system is induced.

Next, additional optimization to the system 10 can be achieved if themethods and systems integrate additional client processes. For instance,the method may further include steps of instructing (FIG. 11, step S42,S60) to trigger additional processes to dissipate heat from thecollector thermal storage. This is preferably decided at step S42, if aheat storage threshold of the collector thermal storage 42 is achieved.

The additional processes are preferably a desalination process and/or anadsorption cooling process. More generally, a variety of clientprocesses can be integrated, e.g., a free cooling process or a processto deliver heat for a chemical application and/or process, etc. However,it can be realized that combining present systems/methods with adesalination process or an adsorption (e.g., water adsorption) coolingprocess has more value in context such as contemplated in presentembodiments, i.e., the higher the solar radiation levels, the morevalued is the output of a desalination or a cooling process.

Moreover, as depicted in FIG. 10, the system 10 may further include afirst heat circuit 71 (typically closed-loop), connecting the PV moduleto a PV thermal storage 41, wherein the latter is distinct from thecollector thermal storage 42. The PV thermal storage 41 and circuit 71are used to cool the PV module (use can for instance be made of acooling device 25 such as described in section 2.1). A second heatcircuit 72 (typically closed-loop too) is also provided, distinct fromthe first heat circuit 71, which connects the collector thermal storage42 to the thermal collector 22. Components 41, 42 also appear in FIGS.14 and 15.

Note that in variants, the system may include a heat circuit connectingboth the PV module and the thermal collector to a thermal storage, inseries, such that fluid in a single heat circuit first reaches thephotovoltaic module to cool it down and then reaches the thermalcollector.

Any of the heat circuits contemplated herein (a single heat circuit whenusing only one circuit or one of or both the two circuits when usingdistinct heat circuits) could additionally be used to cool any componentin the system. Accordingly, part or all of the components that dissipateheat can be included in the loop, such as to contribute to the energyconversion efficiency of the system.

Next, the system may further include a heat exchanger 61, as shown inFIG. 14. The exchanger 61 is thermally connected to the PV storage 41.Accordingly, it can be instructed to provide heat stored in PV storage41 to a thermal user 64, via the heat exchanger 61.

Advantageously, heat exchanger 61 is further thermally connected to thecollector thermal storage 42. In that case, it can be instructed toprovide additional heat stored in the thermal collector storage 42 tothe heat exchanger 61, while providing heat stored in the PV storage 41to the thermal user 64, via exchanger 61.

Heat exchanger 61 may actually include two heat exchangers in series: afirst one lifts up temperature and a second one transfers heat to theuser. The second heat exchanger can be an integral part of the thermaluser 64.

As illustrated in FIG. 14, the system 10 may further include anadditional heat exchanger 63, thermally connected to heat engine 62 andthermal user 64. Advantageously, a thermal user 64 (desalination,adsorption heat pump) is furthermore thermally connected to the PVthermal storage 41. It can furthermore be connected to collector thermalstorage 42, via heat exchanger 61. Then the method may additionallyinclude a step of instructing (FIG. 11, S60) the heat engine to start aprocess of thermal-to-electrical conversion of heat stored in thecollector thermal storage 42, using heat exchanger 63 as a lowtemperature pool.

The additional heat exchanger 63 may be connected to the heat engine 62and the thermal user 64 to provide the low temperature pool for theRankine cycle. For example: a saline feed can be directly inputted touser 64 (step S64, FIG. 14), in which case the Rankine cycle may use airas a low temperature pool; or the saline feed may pass through heatexchanger 63 (preferred option, step S63, FIG. 14) and thus serves asthe low temperature pool to increase a difference of temperature for theRankine cycle.

At present, a complete description of the method of FIG. 11 is given.FIG. 11 corresponds to a particular embodiment, combining many aspectsof the methods discussed above:

Step S10: solar radiation is received on the thermal collector and/orthe PV module;

Step S10: the actual P_(O) is compared to the power demand P_(D), thanksto data relating to the a power demand as received at step S80 (e.g.,power demand may vary rapidly; a corresponding data flow may be receivedand processed at unit 100, FIG. 20). In particular, if it appears thatP_(O)>P_(D), the process goes to S30. As stated, this comparison ispreferably subject to ad-hoc tolerance and possibly a timer, to avoidtoo frequent actuations. If this condition is not fulfilled (P_(O) isnot larger than P_(D)), the process goes to S22;

Step S30: as P_(O)>P_(D), positioning mechanism are instructed to movethe photovoltaic module and/or the thermal collector, to decrease theradiation intensity ratio and thereby favor radiation collected at thethermal collector;

Step S22: unit 100 tests whether P_(O)≈P_(D), in which case P_(O) can bedispatched, step S24, to meet the current power demand (P_(O)=P_(d)). Ifnot, the process goes to S50;

Step S50: unit 100 checks whether heat stored in storage 42 issufficient to start a thermal-to-electrical conversion and thereby meetthe power demand P_(D);

Step S56: if yes, the thermal-to-electrical conversion process isstarted; electrical power accordingly produced can then be dispatched,step S57, to meet the current power demand. If necessary, the electricalpower obtained by thermal-to-electrical conversion may be “added” to thePV power available P_(O) to meet the demand. Yet, the “size” of thethermoelectrical converter shall typically be 10-20% of the maximalpower that the CPVT system can deliver. This, in practice, is enough tosatisfy demand overnight but not during day.

Step S52: If not (i.e., if the heat stored in storage 42 is notsufficient to start a thermal-to-electrical conversion), then theprocess shall fail to meet the demand. Yet, the available PV power cannonetheless be delivered;

Step S40: since at step S30, positioning mechanism may have moved thephotovoltaic module and/or the thermal collector to favor radiationcollected at the thermal collector, heat can conveniently be stored(step S40). The current level of heat as stored at S40 is used as inputfor S50;

Step S42: on the other hand, if the storage capacity appears to beachieved (as monitored at S42), unit 100 may instruct to start anadditional, client process (e.g., free cooling, desalination, adsorptioncooling, etc.): the process goes to S60. Now, if the storage capacity isnot achieved yet, additional heat can be stored, step S40.

Following this principle, a particular efficient scenario is nowdescribed, referring notably to FIG. 14. Heat is collected from themicrochannel cooler (FIG. 1-5, ref. 25) into a low grade heat tank 41(FIG. 14), by way of heat circuit 71 (71 i, 71 o). Heat is furthercollected from the homogenizer 74 (FIG. 9) and thermal collector 22(FIG. 9) into a high-grade heat tank 42 (FIG. 14), thanks to circuit 72(72 i, 72 o). The low grade heat tank directly feeds power user, namelya desalination system (membrane distillation) 64. Additional heatexchanger 61 can lift the temperature using heat from the high gradetank when the low-grade heat tank is partially or fully depleted. Thehigh grade heat tank feeds a Rankine process 62 to convert heat intoelectrical power with an efficiency of 20-30%. The low temperature poolis derived from the incoming salt water S63 or from an air cooler S64(FIG. 14).

FIG. 15 shows another possible configuration for the system 10, whoseunderlying scheme allows for managing both electrical power and waterdelivery on demand. FIG. 15 shows:

The same components 20, 41, 42, 62 and 64 as in FIG. 14, except that thedesalination system includes 64, 64 a and 65. Reference 64 nowcorresponds to the desalination process, 64 a is the corresponding feedof the process 64, and 65 refers to a desalination water storage. Thedesalination water storage 65 is connected to the desalination process64 to provide water 66 on demand;

A heat exchanger 63 a, which is connected to feed 64 a of thedesalination system and to the Rankine process 62, itself connected toboth storages 41 and 42 as before. Note that heat exchanger 63 a in FIG.15 plays a similar role as heat exchanger 63 in FIG. 14;

The first heat circuit 71 connects to the first storage 41 as before.The circuit now branches to the desalination process 64 (via circuitportion 71 b), which is otherwise aided by the storage 41 (via circuitportion 71 c). Circuit portion 71 c may include a heat exchanger, ifneeded.

The above system allows for providing both electrical power 10 a andwater delivery 66 on demand, making optimal use of high and low gradeheat tanks.

Methods as described hereinbefore are all the more efficient if thetemperature in the collector thermal storage 42 is substantially largerthan the temperature in the PV thermal storage 41, i.e., more than 20°C. However, a temperature difference of more than 30° C. substantiallyimprove performances of the systems. Ideally, temperatures differ bymore than 50° C., a thing that can be achieved in embodiments asdescribed herein.

The hybrid receiver 20 is preferably movably mounted in the system 10,such that positioning mechanism 30 can move the receiver 20 as a whole(e.g., the photovoltaic module and the thermal collector are not movableindependently from each other by the positioning mechanism), by simpletranslation along the optical axis, as described in section 2.2. Thissubstantially simplifies the design of the system. In addition, thisallows for integrated solutions that efficiently capture heat dissipatedby the various components of the receiver 20, e.g., via circuit 72. Inturn, the temperature difference between the two circuits 71, 72 can beoptimized.

In variants, only the thermal collector panel 22 a could be moved (thePV module 21 is fixed). For instance: the thermal collector panel mayconsists of essentially a 2D arrangement of thermal circuitsintermingled with an array of lenses, which collector can be moved moreor less close to the fixed PV module. In addition, assuming a homogenousdistribution of the radiation on the photovoltaic receiver, this lattercan be moved relatively to the thermal receiver (or vice versa), intransverse direction to incoming radiation, to cover a section of thephotovoltaic receiver and accordingly vary the energy captured in thethermal circuit vs. the PV circuit. Accordingly, there are variouspossible ways of embodying a photovoltaic module and/or a thermalcollector movably mounted in the system.

Weather Predictions, Predicted Electricity and Water on Demand

The objective of some of the methods described herein is to provideelectricity on demand and at the same time fulfill other core demands ina sunny location based on medium/high grade heat delivered by the solarCPVT receiver: e.g., desalinated water and cooling. Desalination and/orcooling can be operated directly or from stored heat. A sufficienttemperature level for desalination and cooling can be reached thanks tothe above methods. Hot water can be stored during high irradiance, i.e.,exceeding the need for electricity. The coolant from the PV cooling unitis stored in the warm water tank 41 for later use at power users 64(desalination and cooling). When more electrical energy is needed thanavailable from the PV receiver, a low-pressure organic Rankine process62 is activated. A microchannel heat exchanger 25 driven by the storedheat creates vapor that drives a turbine and produces electrical power.

Electrical demand curves in most locations show a peak during noon andtwo smaller peaks in the morning and in the evening. The demand duringthe night is typically 10 times smaller. With an organic Rankinefacility that is 10 times smaller than the peak photovoltaic output thenight time demand, and together with the partial solar power the morningand evening peaks can be covered.

In order to bridge the night about 30% of the daily thermal input iscollected at a high temperature level and converted to electrical powerby a high efficiency low temperature organic Rankine cycle. Heat isstored in a hot water tank during day, together with the lower ambienttemperature at night the Rankine cycle can convert the heat intoelectrical power with a fairly good efficiency. The efficiency of thethermal—electrical conversion will be improved by use of the solarconcentrators to radiate thermal energy to space at low or negativeCentigrade temperatures. Since thermal desalination provides a relativevalue that is more than 30% of the electrical output, it can be realizedthat it is the ideal candidate for a controlled output power station.Thermal desalination processes can be easily regulated by a factor offour and delivery of desalinated water can be on-demand when a largeoutput water storage tank is used.

To allow a concentrated photovoltaic thermal system to store a weekworth of energy for desalination and electrical energy generation atreasonable prices two separate storage tanks are needed: (i) a ˜5000 m³per MW warm water atmospheric pressure storage pool and a ˜1000 m³pressurized hot water storage tank. The warm water pool stores the 90°C. heated coolant from the PV microchannel coolers whereas the hot watertank stores the 150° C. coolant from the thermal collector(panel+homogenizer). In variants, a single low pressure tank with avolume of ˜5000 m³ is needed for a sequential cooling system (circuits71 and 72 in series) that operates at ˜120° C. and 2 bars. The hot waterstorage can be used to drive a low-pressure organic Rankine enginewhereas the warm water storage tank is used to drive the membranedesalination or adsorption cooling processes (FIG. 14). A heat exchangeris devised to extend the capacity of the warm water tank and thedesalination capacity by a factor of two in case electrical demand islow. Both tanks use a layered storage approach to prevent temperaturedrops in partially filled tanks.

More problematic are periods of bad (rainy) weather where the directsolar radiation is very small. Fortunately, the demand for desalinatedwater or cooling during these periods is negligible. This means thewhole thermal storage can be converted to electricity using the organicRankine facility. With improved computer modeling weather prediction hasbecome accurate over a period of five days, i.e., a period for whichthermal storage can be achieved.

The efficiency of the thermal—electrical conversion will be improved byuse of solar concentrators to radiate thermal energy to space at low ornegative Centigrade temperature.

Referring to FIGS. 19 and 20: for areas with multiple solar powerstations the stations that face the wind direction can serve asradiation predictors for the subsequent power stations. This allows amore accurate short term dispatching of the electrical power. Forsituations with upcoming larger clouds the desalination production isreduced in favor of thermal storage to have enough capacity for Rankinepower generation. The control facility 100 to perform such functions canbe automated. Movement speed and direction of clouds can be measured bydetecting the covering speed and direction on the different receiversfor an upcoming cloud. The measurement is performed by e.g., thequadrant detector that is already part of the two axis trackers. Suchinputs are then fed into the control system 100 to determine thetrajectory of the cloud and determine whether and when a neighboringpower station will be affected. This monitoring can be performedcontinuously. Outside of the main production zone 300 scattered“metrology” receiver arrays 301-303 are placed that may supply singlehouses or small villages but mainly serve as “early warning” stationsfor the appropriate dispatching strategy of the main power stations.These arrays have to be large enough to be able to detect cloud speedand direction.

Next, the control system 100 can be designed to tune the buffered energycorresponding to weather predictions. The capability planning of thepower-station is now coupled with weather forecast. Before a predictedrainfall, desalination can be reduced to accumulate heat for productionof electricity, in order to bridge the absence of direct solar radiationduring the rainfall period. This is easily compensated due to the lowerdemand for water during rainy periods. Accumulation of heat andexpansion of thermal storage is accomplished by running the coolanthotter through the CPVT to sacrifice electrical yield.

Specific Implementation Details

Many optional features can be contemplated, some of which have alreadybeen evoked above. To start with, the thermal collector 22 and PV module21 may be embodied such as described in section 2.2. Similarly, thereceiver may further include minor elements 74, such as depicted inFIGS. 6-7. The latter are provided in an intermediate section 75 (FIG.9) and preferably thermally connected to the collector thermal storage42, by a same circuit 72 that connects the thermal collector 22 to thecollector thermal storage 42. The receiver may also include: a band passfilter 76 as described in section 2.2; a concentrator (FIG. 10, 27, 27a, 27 b, 271) having any of the features described in section 2.2.

Concerning operation methods: the feedback algorithm could also be basedon thermal demand, to produce water, refrigeration or feed anotherthermal process, and not only on the power demand. In addition, aRankine engine can run forward and backward, to help to “pump” up thestored heat. Reversible Rankine engine can contribute to grid services,which allows for using the investment in the Rankine engine longer andwith better value.

Additional Technical Implementation Details

Finally, FIG. 20 illustrates an exemplary embodiment of a computerizedunit suitable for implementing aspects of the present invention. It willbe appreciated that the methods described herein are largelynon-interactive and automated. In exemplary embodiments, the methodsdescribed herein can be implemented either in an interactive,partly-interactive or non-interactive system. The methods describedabove can be partly implemented in software (e.g., firmware), hardware,or a combination thereof. In exemplary embodiments, the methodsdescribed herein are implemented in software, as an executable program,and is executed by a special or general-purpose digital computer, suchas a personal computer, workstation, minicomputer, or mainframecomputer. The system 100 therefore includes general-purpose computer101.

In exemplary embodiments, in terms of hardware architecture, as shown inFIG. 20, the computer 101 includes a processor 105, memory 110 coupledto a memory controller 115, and one or more input and/or output (I/O)devices 140, 145 (or peripherals) that are communicatively coupled via alocal input/output controller 135. The input/output controller 135 canbe, but is not limited to, one or more buses or other wired or wirelessconnections, as is known in the art. The input/output controller 135 mayhave additional elements, which are omitted for simplicity, such ascontrollers, buffers (caches), drivers, repeaters, and receivers, toenable communications. Further, the local interface may include address,control, and/or data connections to enable appropriate communicationsamong the aforementioned components. As described herein the I/O devices140, 145 can be any generalized cryptographic card or smart card knownin the art.

The processor 105 is a hardware device for executing software,particularly that stored in memory 110. The processor 105 can be anycustom made or commercially available processor, a central processingunit (CPU), an auxiliary processor among several processors associatedwith the computer 101, a semiconductor based microprocessor (in the formof a microchip or chip set), a macroprocessor, or generally any devicefor executing software instructions.

The memory 110 can include any one or combination of volatile memoryelements (e.g., random access memory, RAM, such as DRAM, SRAM, SDRAM,etc.) and nonvolatile memory elements (e.g., ROM, erasable programmableread only memory (EPROM), electronically erasable programmable read onlymemory (EEPROM), programmable read only memory (PROM), tape, compactdisc read only memory (CD-ROM), disk, diskette, cartridge, cassette orthe like, etc.). Moreover, the memory 110 may incorporate electronic,magnetic, optical, and/or other types of storage media. Note that thememory 110 can have a distributed architecture, where various componentsare situated remote from one another, but can be accessed by theprocessor 105.

The software in memory 110 may include one or more separate programs,each of which includes an ordered listing of executable instructions forimplementing logical functions. In the example of FIG. 20, the softwarein the memory 110 includes methods described herein in accordance withexemplary embodiments and a suitable operating system (OS) 111. The OS111 essentially controls the execution of other computer programs, suchas the methods as described herein, and provides scheduling,input-output control, file and data management, memory management, andcommunication control and related services.

The methods described herein may be in the form of a source program,executable program (object code), script, or any other entity comprisinga set of instructions to be performed. When in a source program form,then the program needs to be translated via a compiler, assembler,interpreter, or the like, which may or may not be included within thememory 110, so as to operate properly in connection with the OS 111.Furthermore, the methods can be written as an object orientedprogramming language, which has classes of data and methods, or aprocedure programming language, which has routines, subroutines, and/orfunctions.

In exemplary embodiments, a conventional keyboard 150 and mouse 155 canbe coupled to the input/output controller 135. Other output devices suchas the I/O devices 140, 145 may include input devices, for example butnot limited to a printer, a scanner, microphone, and the like. Finally,the I/O devices 140, 145 may further include devices that communicateboth inputs and outputs, for instance but not limited to, a networkinterface card (NIC) or modulator/demodulator (for accessing otherfiles, devices, systems, or a network), a radio frequency (RF) or othertransceiver, a telephonic interface, a bridge, a router, and the like.As described herein the I/O devices 140, 145 can be any generalizedcryptographic card or smart card known in the art. The system 100 canfurther include a display controller 125 coupled to a display 130. Inexemplary embodiments, the system 100 can further include a networkinterface 160 for coupling to a network 165. The network 165 can be anIP-based network for communication between the computer 101 and externalservers or clients and the like via a broadband connection. The network165 transmits and receives data between the computer 101 and externalsystems 300, 301, 302, 303. In exemplary embodiments, network 165 can bea managed IP network administered by a service provider. The network 165may be implemented in a wireless fashion, e.g., using wireless protocolsand technologies, such as WiFi, WiMax, etc. The network 165 can also bea packet-switched network such as a local area network, wide areanetwork, Internet network, or other type of network environment. Thenetwork 165 may be a fixed wireless network, a wireless local areanetwork (LAN), a wireless wide area network (WAN) a personal areanetwork (PAN), a virtual private network (VPN), intranet or othersuitable network system and includes equipment for receiving andtransmitting signals.

If the computer 101 is a PC, workstation, intelligent device or thelike, the software in the memory 110 may further include a basic inputoutput system (BIOS) (omitted for simplicity). The BIOS is stored in ROMso that the BIOS can be executed when the computer 101 is activated.

When the computer 101 is in operation, the processor 105 is configuredto execute software stored within the memory 110, to communicate data toand from the memory 110, and to generally control operations of thecomputer 101 pursuant to the software. The methods described herein andthe OS 111, in whole or in part are read by the processor 105, perhapsbuffered within the processor 105, and then executed.

When aspects of the systems and methods described herein are implementedin software, as is shown in FIG. 11, the methods can be stored on anycomputer readable medium, such as storage 120, for use by or inconnection with any computer related system or method.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, the aspects may take the form of an entirelyhardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module” or “system.” Furthermore,aspects of the present invention may take the form of a computer programproduct embodied in one or more computer readable medium(s) havingcomputer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described above with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams can be implemented by computerprogram instructions. These computer program instructions may beprovided to a processor of a general purpose computer, special purposecomputer, or other programmable data processing apparatus to produce amachine, such that the instructions, which execute via the processor ofthe computer or other programmable data processing apparatus, implementthe functions/acts specified in the flowchart and/or block diagram blockor blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart/block diagrams in FIGS. 11, 14 and 15 illustrate thearchitecture, functionality, and operation of possible implementationsof systems, involving methods and computer program products according toembodiments. In this regard, each block in the flowchart or blockdiagrams may represent a module, segment, or portion of code, whichincludes one or more executable instructions for implementing thespecified logical function(s). It should also be noted that, in somealternative implementations, the functions noted in the blocks may occurout of the order noted in the figures. For example, two blocks shown insuccession may, in fact, be executed substantially concurrently, or theblocks may sometimes be executed in the reverse order, depending uponthe functionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts, or combinations of special purpose hardware andcomputer instructions.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation to theteachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.For example: various other manifold layer designs/dimensions/materialscould be relied upon for the cooling devices; various othershapes/dimensions can be contemplated for the thermal panels of thethermal collectors;

Additional components (beyond components mentioned in the presentspecification) may be inserted in the systems of FIGS. 10, 14 and 15.Many usual components have been omitted in the description of thedevices and systems of FIGS. 1-10, 12-15, and 19-20, for the sake ofconciseness.

1. A chip module cooling device, comprising: two fluid circuitscorresponding to an inlet fluid circuit and an outlet fluid circuit,respectively, wherein each of the two fluid circuits comprises anarrangement of orifices and channel portions forming a tree structure,wherein branches of the tree structure represent the orifices, and nodesof the tree structure represent the channel portions, a branch linking anode to one child node only, wherein several nodes having a same parentnode are sibling nodes and extends through L levels of the treestructure, with L≧3, and is in fluidic connection with the other one ofthe two fluid circuits, via channel portions corresponding to leaf nodesof the tree structure; wherein, for each of the two fluid circuits,channel portions corresponding to sibling nodes are parallel to eachother, and are not parallel to a channel portion corresponding to aparent node of the sibling nodes; and wherein channel portions of one ofthe fluid circuits are parallel to and interdigitated with channelportions of the other one of the fluid circuits.
 2. The chip modulecooling device of claim 1, wherein at one or more levels of the treestructure, and for each of the two fluid circuits, channel portionscorresponding to sibling nodes are parallel to channel portionscorresponding to a grandparent node of the sibling nodes.
 3. The chipmodule cooling device of claim 1, wherein at one or more levels of thetree structure, and for each of the two fluid circuits, each of thechannel portions corresponding to sibling nodes extends along adirection which, together with a direction of extension of a parent nodeof the sibling nodes, form a pair of skew lines, and wherein the channelportions corresponding to sibling nodes span a plane parallel to theparent node of the sibling nodes.
 4. The chip module cooling device ofclaim 1, wherein each of the two fluid circuits comprises, at each levelLl of the L levels for which 1≦l≦L−1: Nl orifices of the orifices, eachleading to a respective one of the channel portions; and Nl parallelchannel portions, each of the Nl channel portions enabling fluiddistribution to Bl+1 orifices of the next level, where: Bl+1=Nl+1/Nl;B2≧2 and B3≧2.
 5. The chip module cooling device of claim 4, wherein: ata given level Lm of the L levels, where 2≦m≦L, positions of orifices ofone of the fluid circuits correspond to first discrete points of a firstfinite array, the first discrete points generated by a set of discretetranslations R defined by R=n1 a1+n2 a2, where n1 and n2 are integersand a1 and a2 are linearly independent vectors; channel portions at thelevel Lm−1 extend along or parallel to a1; and channel portions atlevels Lm extend along or parallel to a2; and positions of orifices ofthe other one of the fluid circuits correspond to second discrete pointsof a second finite array, translated from the first finite array by atranslation r defined by r=x1 a1+x2 a2, with 0<x1<1 and 0≦x2<1, andx1=x2=½.
 6. The cooling device of claim 4, wherein each of the two fluidcircuits comprises, in at least one level Ll of the L levels: Nl channelportions forming Ncl strictly parallel channel lines, with Bl≦Ncl≦Nl,each of the Ncl channel lines comprising channel portions arrangedin-line, and wherein preferably Ncl=Bl.
 7. The cooling device of claim6, wherein each of the two fluid circuits comprises, at each level Ll ofthe L levels: Nl channel portions forming Bl strictly parallel channellines, each of the channel lines comprising Bl−1 channel portionsarranged in-line, and wherein at one or more of the L levels, channelportions in a given channel line are connected to enable fluidcommunication from one channel portion to another in the given channelline.
 8. The cooling device of claim 7, wherein at a given level Lm ofthe L levels, where 1≦m≦L, Ncl strictly parallel channel lines of theinlet fluid circuit are interdigitated with Ncl strictly parallelchannel lines of the outlet fluid circuit, each channel line of theinlet fluid circuit being parallel to each channel line of the outletfluid circuit.
 9. The cooling device of claim 4, wherein at a givenlevel Lm of the L levels and for each of the two fluid circuits, atleast some of the Nm channel portions have a non-constant cross-section,and preferably comprise an enlarged area vis-à-vis a respective one ofthe Nm orifices.
 10. The cooling device of claim 4, wherein: at a givenlevel Lm of the L levels, two sets of orifices, each comprising Bmorifices, are arranged in correspondence with respective outermostchannels of a previous level Lm−1; and each of the Bm orifices of thetwo sets and/or each of their respective channel portions have reduceddimensions along a direction of extension of the channels of level Lm.11. The cooling device of claim 1, further comprising a heat transferstructure, configured to connect one of the fluid circuits to the other,wherein the heat transfer structure preferably comprises silicon. 12.The cooling device of claim 11, wherein the heat transfer structurecomprises heat transfer channel portions, each of the heat transferchannel portions connecting at least one channel portion correspondingto a leaf node of the inlet fluid circuit to one channel portioncorresponding to a leaf node of the outlet fluid circuit, and wherein,preferably, each heat transfer channel extends along a directionrotated, preferably by 90°, with respect to a direction of extension ofthe channel portions that it connects.
 13. The cooling device of claim1, wherein a cumulated width of the cross-sectional areas of allorifices of one of the levels is substantially equal, subject to ±15%,to a cumulated width of the cross-sectional areas of all orifices ofanother one of the levels, preferably of all other levels.
 14. Thecooling device of claim 13, wherein one or more levels of the L levelscomprise two superimposed layers, a first one of the two superimposedlayers comprising the orifices as through holes, the second one of thetwo superimposed layers comprising channel portions as through holes,and wherein, preferably, the two superimposed layers are made ofdifferent materials.
 15. A photovoltaic receiver, comprising: aphotovoltaic module; and a cooling device, thermally connected to thephotovoltaic module, the cooling device comprising two fluid circuitscorresponding to an inlet fluid circuit and an outlet fluid circuit,respectively, wherein each of the two fluid circuits comprises anarrangement of orifices and channel portions forming a tree structure,wherein branches of the tree structure represent the orifices, and nodesof the tree structure represent the channel portions, a branch linking anode to one child node only, wherein several nodes having a same parentnode are sibling nodes and extends through L levels of the treestructure, with L≧3, and is in fluidic connection with the other one ofthe two fluid circuits, via channel portions corresponding to leaf nodesof the tree structure; wherein, for each of the two fluid circuits,channel portions corresponding to sibling nodes are parallel to eachother, and are not parallel to a channel portion corresponding to aparent node of the sibling nodes; and wherein channel portions of one ofthe fluid circuits are parallel to and interdigitated with channelportions of the other one of the fluid circuits.